Imprinting

In contrast to altricial animals, precocial species must be able to walk within a short time after birth. However, this ability may result in wandering away from the safety of the mother. Newly hatched domestic fowl, ducks, geese, quail, ungulates, and guinea pigs are precocial. These young animals are dependent on the mother for food, guidance, and protection. Therefore, they must develop an attachment to the mother to ensure they stay with her to increase the probability of survival. Konrad Lorenz, in the 1930s, coined this attachment behavior as imprinting.

Imprinting must occur within a specified time period following birth or hatching. This time period is called the sensitive, or critical, period. In most cases, if the animal does not become imprinted to an object during this critical period, it is highly unlikely that it will develop later. Additionally, Lorenz found that the imprinting affects the future sexual preferences of the animal.

Lorenz examined the imprinting process of young goslings. He found that they imprinted to the first moving object they saw within the first few days of hatching. The moving object could be a ball, a toy soldier, or a person. Lorenz himself became the imprinted object of many Graylag goslings. Other researchers have found that the imprinted figure could also be the one who provides the first feeding, living figures and individuals, female caregivers, and moving objects, whether living or inanimate. Imprinting, therefore, is the mechanism that evolved to produce following behavior. The adaptive function of imprinting is to allow the young animal to distinguish its own mother from other mothers of the same or different species and to remain near her.

Imprinting facilitates future adult social behavior in addition to feeding, guidance, and protection in infancy. Lorenz suggested that the imprinting provides a model for the individual to compare all members of its species against other species. Japanese quail, for example, have been observed to choose sexual mates that are similar to those individuals they were exposed to during the imprinting stage. Although the mates were similar to the imprinted figure, they were not exactly like them. Lorenz and others speculated that this is a mechanism that evolved to reduce the probability of inbreeding. Specifically, in their natural environment, young animals imprint on immediate relatives, typically their mothers. By choosing mates that are somewhat similar to the imprinted figure, the animal is increasing the chance that the mate is unrelated.

Lorenz also believed that imprinting was enhanced by its consequences. When a young chick, duckling, or gosling imprints to its mother, she will provide positive rewards for this behavior. Specifically, she will scratch the dirt for food, guide the young to appropriate shelter, and provide protection from predators. Additionally, laboratory studies have shown that rewarding young birds with food enhances their imprinting behavior. However, food is not the only reward that influences imprinting behavior. Studies have shown that young animals tend to avoid novel objects and exhibit fear responses when around them. Imprinting provides the young animals with a familiar object to approach. The familiar object symbolizes safety and comforting thus reducing anxiety. This reduction of anxiety may be an additional reinforcement for imprinting behavior.

Finally, Lorenz suggested that imprinting is an innate behavior that is genetically programmed to occur when activated by a releaser mechanism. Nikolaas Tinbergen, a colleague who worked closely with Lorenz, suggested that sign stimuli are environmental cues that elicit certain behaviors. In the instance of imprinting, the sign stimuli serve as the releaser mechanism that promotes parental proximity-seeking behavior by newly hatched or born animals.